ISLAMABAD (Reuters) - Pakistan’s anti-corruption agency will open a criminal investigation into former prime minister Nawaz Sharif and current finance minister Ishaq Dar, it said on Thursday.

Sharif was ousted in July after the Supreme Court deemed him unfit to hold office for not declaring a small source of income, and ordered the agency, the National Accountability Bureau (NAB), to instigate a criminal investigation into him, his family and Dar.

The agency said its investigation would rely on the evidence collected by a Supreme Court-appointed six-man panel that was investigating the Sharif family’s wealth and included officers from powerful military intelligence agencies.

“The chairman (of) NAB directed that the prosecution of the cases will be followed up vigorously in the concerned Accountability Courts,” the agency said in a statement.

The three-time premier said he never received the income that investigators said he did not declare.

Sharif has said there was a conspiracy against him but did not identify anyone. Instead, he named long-time loyalist Shahid Khaqan Abbasi as his replacement as prime minister until the next election, expected in mid-2018.

Pakistan has for decades been plagued by pervasive graft, as well as by rivalry between the military and civilian politicians.

The NAB’s conviction rates are notoriously low and Sharif has multiple investigations by the agency pending against him, including one dating back to 1999.

Reporting by Asif Shahzad; Writing by Drazen Jorgic; Editing by Robert Birsel